In many fields it is often necessary to separate different entities at the molecular level. The efficiency of such separations, or even the ability to make the separations at all, is often a determining factor in the feasibility of a particular product or method. Particularly at the industrial scale, there is a need for new and improved processes which facilitate separation, at the molecular level, of closely related molecules in a bulk medium.
A microemulsion is a thermodynamically stable dispersion of one liquid phase into another, stabilized by an interfacial film of surfactant. Microemulsions are typically clear solutions, as the droplet diameter is approximately 100 nanometers or less. The interfacial tension between the two phases is extremely low.
Microemulsions are distinct from (macro)emulsions, which are thermodynamically unstable dispersions of macroscopic droplets of one or more liquid and/or liquid crystalline phases in a continuous liquid. However, a microemulsion may be one of the phases of an emulsion. The microemulsion may appear as one of three phases, for example, a middle phase in simultaneous equilibrium with a top or upper oleic phase, and a bottom or lower aqueous phase. Because the three phases are close to a tricritical point (where all three phases simultaneously become a single phase), the interfacial tensions among the three phases are several orders of magnitude less than the tensions produced by conventional micellar solutions. Moreover, by suitable changes of temperature, salinity, or other compositional variable, the composition of the middle phase can be made to vary continuously between that of the bottom and top phases.
Microemulsions may be oil-in-water, water-in-oil, or bicontinous states of matter characterized by isotropic composition, thermodynamic stability, submicron particle dimension, and transparency. Typically, the elements include an oil, a surfactant (e.g., ionic, nonionic, or both), and a cosurfactant mixed into a bulk media (e.g., water, saline). Because the core of a microemulsion can be be oil, these microemulsions may be useful for molecular separation of hydrophobic molecules from a bulk solution of an aqueous nature into the oil core of each microemulsion nanoparticle. However, because hydrophobic forces nonspecifically apply to all lipophilic molecules, such microemulsions will also partition nontargeted molecules. For example, whereas a microemulsion may sequester a toxic agent from blood, it may also remove other lipophilic agents that are either native (e.g., steroids) or foreign (e.g., injected drugs) and that may be beneficial.
Currently, no way exists to preclude unintended removal of these non-targeted molecules. Thus, these microemulsions cannot distinguish targeted and nontargeted molecules for separation from bulk media. Therefore, a need exists for improved methods for molecular separation.